update the plugin template repo to use javascript rather than mkdocs for their standalone docs sites

[caro401]

Opening this as a separate issue to track work that needs to be done on the plugin template repo https://github.com/DHARPA-Project/kiara_plugin.develop to get a docs build working again

I believe the steps involved are:

• replace the docs folder contents with a new javascript-based docs site
• migrate any existing authored docs content into that new setup
• add commands in the makefile to set up and build the docs using the new javascript-based approach
• add/update a GitHub action, run on creation of a tag, to first create the JSON file for the plugin at that tag's version, then rebuild the docs site and publish to GitHub pages
• remove any dependencies related only to mkdocs

and of course the meta-work of updating the plugin template's changelog, writing docs about how to write/build/publish the autogenerated docs

Because a lot of this involves writing and testing GitHub actions and pages, I'll pull the relevant bits of the plugin template into a separate repo on my account (so I can properly debug/configure GitHub pages, and to spare you all noise from failed builds). Once I've debugged most of the build failures, I'll transfer the work back into the main template repo.

@makkus does this match with your expectations of the approach and the steps involved? The original spec for this work said a SvelteKit-based site, but I think I'd prefer to go Astro/Starlight (with Svelte components from the shared package), to match the main docs site more closely if that's acceptable?